Heat exchanger incorporating a rolled aluminum alloy

ABSTRACT

A heat exchanger incorporating at least one component made from a rolled 6xxx-series aluminium alloy having a composition, in wt. %, of Si 0.2% to 1.3%, Mg 0.3% to 1.3%, Cu up to 0.80%, Fe 0.05% to 1.0%, Mn 0.05% to 0.70%, optionally one or two elements selected from the group 0.05-0.35% Zr and 0.04-0.35% Cr, Zn up to 0.25%, Ti up to 0.25%, balance unavoidable impurities and aluminium, and wherein the Fe/Mn ratio is &lt;1.90.

FIELD OF THE INVENTION

The invention relates to a brazed heat exchanger comprising variouscomponents and at least one component being made from the rolled6xxx-series aluminium alloy product according to this invention. Theinvention relates further to the use of the rolled aluminium alloy in aheat exchanger.

BACKGROUND TO THE INVENTION

Heat exchangers and other similar equipment, such as condensers,evaporators and the like for use in car coolers, air conditioningsystems, industrial cooling systems, etc. usually comprise a number ofheat exchange tubes arranged in parallel between two headers, each tubejoined at either end to one of the headers. Corrugated fins are disposedin an airflow clearance between adjacent heat exchange tubes and arebrazed to the respective tubes. These various components are commonlyjoined to each other done by brazing. In a brazing process, a brazingfiller metal or brazing alloy, or a composition producing a brazingalloy upon heating, is applied to at least one portion of the substrateto be brazed. After the substrate parts are assembled, they are heateduntil the brazing metal or brazing alloy melts. The melting point of thebrazing material is lower than the melting point of the aluminiumsubstrate or aluminium core sheet.

Brazing sheet products find wide applications in heat exchangers andother similar equipment. Conventional brazing products have a core ofrolled sheet, typically an aluminium alloy of the 3xxx-series, having onat least one surface of the core sheet an aluminium clad layer (alsoknown as an aluminium cladding layer). The aluminium clad layer iscommonly made of a 4xxx-series alloy comprising silicon in an amount inthe range of 4% to 20%, and preferably in the range of about 6% to 14%.The aluminium clad layer may be coupled or bonded to the core alloy invarious ways known in the art, for example by means of roll bonding,cladding spray-forming or semi-continuous or continuous castingprocesses. These aluminium clad layers have a liquidus temperaturetypically in the range of about 540° C. to 615° C.

Although commercially sold brazing sheet products have predominantly acore alloy based on a 3xxx-series aluminium alloys, there arecommercially available brazing sheet products having a heat-treatable6xxx-series aluminium alloy as core alloy. These 6xxx-series alloys canbe used also base plate of a heat exchanger or for manufacturing headersor side plates of a heat exchanger. Within the 6xxx-series alloys thealloys AA6101, AA6151, AA6951, AA6060, AA6061, and AA6063 can be found.A list of the key alloying elements of these alloys is given in Table 1.

TABLE 1 Alloy composition (in wt. %) of several prior art rolledaluminium alloys used in heat exchangers and as registered with theAluminium Association. Element Alloy Mg Si Fe Cu Mn Cr AA6101 0.35-0.80.30-0.70 <0.50 <0.10 <0.03 <0.03 AA6151 0.45-0.8 0.6-1.2 <1.0 <0.35<0.20 0.15-0.35 AA6951 0.40-0.8 0.20-0.50 <0.8 0.15-0.40 <0.10 — AA60600.35-0.6 0.30-0.6  0.10-0.30 <0.10 <0.10 <0.05 AA6061  0.8-1.2 0.40-0.8 <0.7 0.15-0.40 <0.15 0.04-0.35 AA6063 0.45-0.9 0.20-0.6  <0.35 <0.10<0.10 <0.10For each alloy the balance is made by Zn as an impurity (commonly <0.25%or lower) and Ti (commonly <0.15% or lower), unavoidable impurities andthe remainder is aluminium.

There is a need for improved rolled aluminium alloy products based onthe 6xxx-series aluminium alloys for use in heat exchangers.

DESCRIPTION OF THE INVENTION

As will be appreciated herein, except as otherwise indicated, aluminiumalloy designations and temper designations refer to the AluminiumAssociation designations in Aluminium Standards and Data and theRegistration Records, as published by the Aluminium Association in 2015and are well known to the person skilled in the art. The temperdesignations are laid down in European standard EN515.

For any description of alloy compositions or preferred alloycompositions, all references to percentages are by weight percent unlessotherwise indicated.

As used herein, the term “about” when used to describe a compositionalrange or amount of an alloying addition means that the actual amount ofthe alloying addition may vary from the nominal intended amount due tofactors such as standard processing variations as understood by thoseskilled in the art.

The term “up to” and “up to about”, as employed herein, explicitlyincludes, but is not limited to, the possibility of zero weight-percentof the particular alloying component to which it refers. For example, upto 0.3% Ti may include an alloy having no Ti.

It is an object of the invention to provide a heat exchangerincorporating at least one component made from an improved rolled6xxx-series aluminium alloy.

These and other objects and further advantages are met or exceeded bythe present invention providing a brazed heat exchanger incorporating atleast one component made from a rolled 6xxx-series aluminium alloyhaving a composition, and wherein the rolled 6xxx-series aluminium alloyhas a composition of: Si 0.2% to 1.3%, Mg 0.3% to 1.3%, Cu up to 0.80%,Fe 0.05% to 1.0%, Mn 0.05% to 0.70%, optionally one or two elementsselected from the group of 0.05-0.35% Zr and 0.04-0.35% Cr, Zn up to0.25%, Ti up to 0.25%, balance unavoidable impurities and aluminium, andwherein the Fe/Mn ratio is <1.90.

In accordance with the invention it has been found that the rolled6xxx-series aluminium alloy forms one of the components of a heatexchanger device and the rolled aluminium alloy used provides a goodbalance in post-braze mechanical properties and enhanced corrosionresistance, in particular after long term exposure at elevatedtemperatures, for example for 1,000 hours at 150° C., reflecting longterm use of such a heat exchanger device. This would also allow somedown-gauging of the heat exchanger component made from this 6xxx-seriesalloy.

The purposive combined addition of Mg and Si strengthens the aluminiumalloy due to precipitation hardening of elemental Si and Mg₂Si formedunder the co-presence of Mg. In order to provide a sufficient post-brazestrength level in the core sheet product the Si content should be atleast 0.20%, and preferably at least 0.25%. A preferred upper-limit forthe Si content is about 0.8%, and more preferably about 0.60%, and morepreferably about 0.55%. The presence of Si enhances also theformability.

Substantially for the same reason as for the Si content, the Mg contentshould be at least 0.3%, and preferably at least about 0.35%, and morepreferably at least 0.40% to provide sufficient strength to the rolledproduct. A preferred upper-limit for the Mg content is about 0.9%, andmore preferably about 0.8%.

Fe is not a desired component of the aluminium alloy, but its presenceis normally unavoidable. The Fe-content should not exceed 1.0%, and apreferred upper-limit is about 0.8%, and more preferably about 0.50%. Apreferred range is 0.05% to about 0.40%, and more preferably from about0.10% to about 0.40%, because alloys containing less Fe are moreexpensive.

The presence of substantial amounts of Fe in the aluminium alloy has anadverse effect on the post-braze corrosion resistance. However, it hasbeen found that the purposive effect of Mn to the aluminium alloy maysignificantly improve the post-braze corrosion resistance, for examplethe resistance to intergranular corrosion (IGC), in particular afterlong term exposure at elevated temperature and it increases thepost-braze strength via solid solution hardening. Where 6xxx-seriesaluminium alloy according to the prior art and used in heat exchangersmay have a presence of some Mn, it is referred to only by an upper-limitand thereby clearly suggesting that it is a tolerable impurity and theskilled person is expected to work at the lower-end of any disclosedMn-range. In the aluminium alloy used according to this invention atleast 0.05% Mn must be present. Preferably at least 0.08% Mn is present,and more preferably >0.10% Mn. A preferred upper-limit is about 0.50%,and more preferably about 0.40%. However, it is an important aspect ofthe invention that the Fe/Mn ratio is being controlled and theFe/Mn-ratio should not exceed 1.90, and preferably does not exceed 1.80,and more preferably does not exceed 1.75. A preferred lower-limit forthe Fe-Mn ratio is about 0.7.

Cu may increase the post-braze strength of the aluminium alloy, but itspresence should not exceed 0.80%. It is preferred that the Cu-level doesnot exceed about 0.4%. Cu levels above about 0.4% may rise to a reducedpost-braze corrosion resistance of products incorporating the aluminiumalloy according to the invention.

Ti may be present up to about 0.25% to act as a grain refining additiveduring the casting of an ingot of the aluminium alloy of the invention.Additional Ti may be added, for example due to their presence in scrapmaterial, in order to increase the strength of the core alloy bysolubility hardening. The total amount of Ti present in the alloy shouldpreferably not exceed about 0.20%, but preferably is less than about0.12%. A preferred lower limit for the Ti addition is about 0.01%. Tican be added as a sole element or with either boron or carbon as knownin the art serving as a casting aid, for grain size control.

The Zn content in the aluminium alloy is present as a tolerable impurityelement of less than about 0.25%, and preferably should be present atthe lower-end of this range, e.g. less than about 0.15%, and morepreferably less than about 0.10%, to maintain corrosion resistance atdesired levels.

To the aluminium alloy one or two dispersoid forming elements selectedfrom the group consisting of about 0.05% to about 0.35% Zr and about0.04% to about 0.35% Cr can be added to further improve the strength ofthe aluminium alloy product in the post-braze condition.

A more preferred Zr level is in the range of about 0.05% to about 0.20%,and more preferably in a range of about 0.06% to about 0.15%.

A more preferred Cr level is in the range of about 0.05% to about 0.20%,and more preferably in a range of about 0.06% to about 0.25%.

Preferably, if added to the aluminium, the total combined amount of allthe dispersoid forming alloying elements Zr and Cr does not exceed about0.35% to avoid the formation of coarse constituent particles inparticular when combined with a relative high Fe content in combinationwith the purposive addition of Mn. Coarse constituent particles may havean adverse effect on formability and they may hinder furtherdown-gauging of the product form and they can have an adverse effect onthe corrosion resistance.

In an embodiment of the aluminium alloy it has no purposive addition ofvanadium such that, if present, it is at a level of less than about0.05%, and more preferably less than about 0.03%, such that thealuminium alloy is substantially free from V. With “substantially free”or “essentially free” is meant that no purposeful addition was made tothe chemical composition but that due to impurities and/or leaking fromcontact with manufacturing equipment, trace quantities of V maynevertheless find their way into the alloy product. For example, lessthan about 0.02% is an example of a trace quantity. The aluminium alloymay have 0% V.

The aluminium alloy may contain normal and inevitable impurities,typically each <0.05% and the total <0.2%, and the balance is made byaluminium.

In an embodiment of the invention the 6xxx-series core alloy has acomposition consisting of, in wt. %: Si 0.2% to 1.3%, Mg 0.3% to 1.3%,Cu up to 0.80%, Fe 0.05% to 1.0%, Mn 0.05% to 0.70%, optionally one ortwo elements selected from the group 0.05%-0.35% Zr and 0.04%-0.35% Cr,Zn up to 0.25%, Ti up to 0.25%, balance unavoidable impurities andaluminium, and wherein the Fe/Mn ratio is <1.90, and with preferrednarrower alloy compositions are herein described.

In a preferred embodiment of the invention the rolled 6xxx-seriesaluminium alloy is employed as a bare or non-clad rolled product in theheat exchanger such that in use the outer-face of the aluminium alloy isexposed to the corrosive environment, in particular as a so-called baseplate where the heat exchanger apparatus is brazed onto. In thisembodiment the thickness of rolled 6xxx-series alloy is in a range ofabout 1 mm to 12 mm.

In another embodiment the rolled 6xxx-series aluminium alloy has a firstside and a second side, and at least one clad layer applied on the firstside or the second side. There can be provided a clad layer on both thefirst side and the second side. The at least one clad layer can be a1xxx-series, e.g. AA1050, or a 7xxx-series alloy to provide sacrificialprotection of the 6xxx-series alloy. A suitable 7xxx-series alloy wouldhave a Zn-content of up to about 3%, and would include an AA7072-seriesalloy.

The clad material could also be made from a brazing material andpreferably made of a 4xxx-series aluminium alloy. Typical alloys withinthis series are AA4343, AA4045, AA4047, AA4004, AA4104, AA4147, or somenear compositional variants thereof. The 4xxx-series alloy may furthercontain one or more selected from the group consisting of Zn, In, andSn, in a concentration tailored to effect a desired electrochemicalpotential within and adjacent to a brazing joint.

In accordance with the invention the rolled 6xxx-series alloy can be inthe form a brazing sheet material wherein the 6xxx-series alloy formsthe core alloy material and at least one side is clad with a brazingmaterial, preferably a 4xxx-series alloy. Preferably such a brazingsheet material would be used for manufacturing a brazed tube as one ofthe components of the heat exchanger.

In a further embodiment of the invention, the 6xxx-series core alloy andthe clad brazing material, preferably a 4xxx-series, are separated by aninterliner or an interlayer, such that the core is bonded to aninterliner, and the interliner is, in turn, bonded to the 4xxx-seriesalloy. This structure minimizes localized corrosion, promotes goodbrazeability, reduces liquid film migration, and, by suitable selectionof the interliner alloy, enhances corrosion resistance, such that theinterliner alloy sacrificially protects the underlying core alloy. Anexample of a suitable interliner would be an 1xxx- or 3xxx-series alloy,or a 1xxx- or 3xxx-series alloy with a purposive addition of Zn belowabout 3%, or a purposive addition of In below about 1%.

In another embodiment of such a brazing sheet product there is proved acore alloy bonded on both sides to an interliner, and each interlineris, in turn, bonded to a 4xxx-series alloy.

In another embodiment of the brazing product there is provided anouterliner or waterside liner bonded on one side of the core alloy and aclad brazing material bonded to the other side of the core alloy.Optionally there may be provided an interliner between the 6xxx-seriescore alloy and the clad brazing material. The outerliner would generallybe of an alloy tailored to provide high corrosion resistance or evencorrosion combined with erosion resistance in the environment to whichthat face of the sheet is exposed. An example of a suitable outerlinerwould be an aluminium alloy having a purposive addition of Zn up toabout 3%, such as for example an AA7072-series alloy.

The thickness of the core layer (in percent compared to the totalthickness of the brazing sheet product) of the brazing sheet ispreferably in a range of about 60% to 90%, the thickness of theinterliner or interlayer or outerliner or waterside liner (in percentcompared to the total thickness of the brazing sheet product) ispreferably in a range of about 5% to 25% and the thickness of the cladbrazing layer is preferably (in percent compared to the total thicknessof the brazing sheet) in a range of about 4% to 15%. The thickness ofthe 6xxx-series core alloy at final clad composite gauge can be aslittle as about 80 microns to as much as about 5 mm.

In an embodiment of the invention the one component made from the rolled6xxx-series alloys, either as a clad-product or a non-clad product,forms a base plate, a header or a side support of a heat exchanger. Inthis embodiment the thickness of rolled 6xxx-series alloy is in a rangeof about 1 mm to 12 mm.

In a preferred embodiment the one component made from the rolled6xxx-series alloys, either as a clad-product or a bare or non-cladproduct, forms a base plate of a heat exchanger, more preferably of anoil cooler.

The rolled 6xxx-series aluminium product is preferably provided in afully-annealed “O” temper or an “F” temper or in an “H” temper, i.e. inan H1 or H2 temper. An H1 temper means that the alloy product is strainhardened. An H2 temper means that the alloy product is strain hardenedand partially annealed. In some embodiments, the alloy part may bestrain hardened in accordance with typical H1X or H2X temper practices,where X is a whole number from 0 to 9, e.g. H12 or H24 temper.

The rolled aluminium alloy used in the heat exchanger according to thisinvention is being cast into rolling feedstock, for example by means ofDC-casting or continuous strip casting, and thereafter preferablyhomogenized prior to being down gauged by means of rolling to finalgauge, for example by hot rolling and optionally also by cold rolling.Ideally during the casting process of the rolling stock there is no orvery little formation of β-AlFeSi particles due to the purposiveaddition of Mn and by maintaining the Fe/Mn to less than 1.90. However,where the formation of β-AlFeSi can't be avoided a homogenizationheat-treatment assists in converting any β-AlFeSi to the less harmfulα-AlFeSi form, preferably below 10 μm long and with 90% below 5 μm. Thepurposive addition of Mn acts to accelerate the β- to α-AlFeSitransformation in particular during homogenization so that the resultinghomogenized ingot results in an increased post-braze corrosionresistance when used as a core alloy for a brazing sheet product or whenused as base plate, a header or a side support of a heat exchanger. Theas-cast rolling ingot is also homogenized to bring favourably thesoluble secondary magnesium-silicon phases into suitable form.

The homogenisation heat-treatment involves heating the ingot for atleast about 2 hours, and more preferably at least about 6 hours. Apreferred upper-limit for the homogenisation soaking time is about 48hours, and more preferably about 24 hours. A longer homogenisation timeis not disadvantageous, but is not required and only serves to raise thecosts of production. Homogenisation is preferably performed at atemperature of 525° C. or more using one or more homogenisation steps,more preferably at least one homogenisation step is performed at atemperature range of 540° C. to 600° C. The heat-up rates that can beapplied are those which are regular in the art. Preferably, thealuminium alloy is homogenised for at least about 6 hours and preferablyless than about 20 hours at a temperature range of about 550° C. toabout 600° C.

The present invention also relates to the use or a method of use of therolled 6xxx-series aluminium alloy as described herein, either as a bareproduct or having at least one clad layer on one of its sides, for usein a heat exchanger. Preferably the alloy forms a base plate, a headeror a side support of said heat exchanger. In particular the heatexchanger is a radiator, an oil cooler, an inter cooler, a heater core,an evaporator, a charge air cooler, or a condenser or similarapplications and assemblies which are produced by joining brazing sheetsfor forming a compact assembly, mainly for the purpose of exchangingheat. The rolled 6xxx-series aluminium alloy is particularly useful forhigh performance, light weight, automotive heat exchangers but could beused for other brazed applications including but not limited torefrigeration and HVAC.

The invention shall also be described with reference to the appendedFIG. 1 showing a drawing of the construction of a stacked plate oilcooler in a partially exploded illustration.

FIG. 1 shows schematically an example of the construction of a stackedplate oil cooler 1 which is constructed from a multiplicity of stackingplates 2 and metal turbulence plates 3 (turbulence inserts) arrangedbetween said stacking plates 2. The stacked plate oil cooler 1 is closedoff by means of a base plate 4 and a cover plate 5. An intermediatemetal plate 6 is inserted between the uppermost metal turbulence plate 3and the cover plate 5. Connections for the oil and a liquid coolant arearranged in the relative thick base plate 4, but cannot be seen or arenot illustrated in this FIG. 1. In contrast, the cover plate 5 isclosed; it has, in this embodiment, stamped impressions 10, 12. In thisexample the base plate 4 can be made of the rolled 6xxx-series aluminiumalloy according to the invention providing a good balance in post-brazemechanical properties and enhanced corrosion resistance, in particularafter long term exposure at elevated temperatures, for example for 1,000hours at 150° C., reflecting long term use of such a heat exchangerdevice.

Having now fully described the invention, it will be apparent to one ofordinary skill in the art that many changes and modifications can bemade without departing from the spirit or scope of the invention asherein described.

1. A heat exchanger incorporating at least one component made from arolled 6xxx-series aluminium alloy having a composition, in wt. %, of Si0.2% to 1.3%, Mg 0.3% to 1.3%, Cu up to 0.80%, Fe 0.05% to 1.0%, Mn0.05% to 0.70%, optionally one or two elements selected from the group0.05-0.35% Zr and 0.04-0.35% Cr, Zn up to 0.25%, Ti up to 0.25%, balanceunavoidable impurities and aluminium, and wherein the Fe/Mn ratio is<1.90.
 2. A heat exchanger according to claim 1, wherein the rolled6xxx-series aluminium alloy has a Fe-content of maximum 0.8%.
 3. A heatexchanger according to claim 1, wherein the rolled 6xxx-series aluminiumalloy has a Mn-content of maximum 0.50%.
 4. A heat exchanger accordingto claim 1, wherein the rolled 6xxx-series aluminium alloy has aSi-content of maximum 0.80%.
 5. A heat exchanger according to claim 1,wherein the rolled 6xxx-series aluminium alloy has a Mg-content of atleast 0.40%.
 6. A heat exchanger according to claim 1, wherein therolled 6xxx-series aluminium alloy has a Mg-content of not more than0.9%.
 7. A heat exchanger according to claim 1, wherein the rolled6xxx-series aluminium alloy has a Cu-content of up to 0.4%.
 8. A heatexchanger according to claim 1, wherein the rolled 6xxx-series aluminiumalloy has been homogenized.
 9. A heat exchanger according to claim 8,wherein the 6xxx-series core alloy has been homogenized for up to 48hours at a temperature in a range of 525° C. to 600° C.
 10. A heatexchanger according to claim 1, wherein the rolled 6xxx-series aluminiumalloy has a Fe/Mn ratio of <1.80.
 11. A heat exchanger according toclaim 1, wherein the rolled 6xxx-series aluminium alloy has a first sideand a second side, and at least one clad layer on the first side or thesecond side.
 12. A heat exchanger according to claim 11, wherein the atleast one clad layer is made from an alloy selected from the groupconsisting of a 1xxx, 4xxx, and 7xxx-series aluminium alloy.
 13. A heatexchanger according to claim 1, wherein the rolled 6xxx-series aluminiumalloy is non-clad.
 14. A heat exchanger according to claim 1, whereinthe at least one component made from the rolled 6xxx-series aluminiumalloy forms a base plate, a header or a side support of the heatexchanger.
 15. A heat exchanger according to claim 14, wherein the atleast one component made from the rolled 6xxx-series aluminium alloy hasa thickness in a range of 1 mm to 12 mm and forms the base plate, theheader or the side support of the heat exchanger.
 16. A heat exchangeraccording to claim 1, wherein the at least one component made from therolled 6xxx-series aluminium alloy is provided in a fully annealedO-temper.
 17. A heat exchanger according to claim 1, wherein the atleast one component made from the rolled 6xxx-series aluminium alloy isprovided in a H1X-temper or H2X-temper.
 18. A heat exchanger accordingto claim 1, wherein the at least one component made from the rolled6xxx-series aluminium alloy is provided in an F-temper.
 19. A heatexchanger according to claim 1, wherein the heat exchanger is anautomotive heat exchanger.
 20. A heat exchanger according to claim 1,wherein the heat exchanger is a radiator, a condenser, an evaporator, anoil cooler, an inter cooler, a charge air cooler or a heater core.
 21. Amethod of use of a rolled aluminium alloy as defined in claim 1,comprising forming the alloy into a component in a heat exchanger, as abase plate, a header or a side support in said heat exchanger.
 22. Aheat exchanger according to claim 1, wherein the rolled 6xxx-seriesaluminium alloy has maximum 0.50% Fe.
 23. A heat exchanger according toclaim 1, wherein the rolled 6xxx-series aluminium alloy has maximum0.40% Mn.
 24. A heat exchanger according to claim 1, wherein the rolled6xxx-series aluminium alloy has maximum 0.60% Si.
 25. A heat exchangeraccording to claim 1, wherein the rolled 6xxx-series aluminium alloy hasnot more than 0.8% Mg.
 26. A heat exchanger according to claim 1,wherein the rolled 6xxx-series aluminium alloy Fe/Mn ratio is <1.75. 27.A heat exchanger according to claim 1, wherein the rolled 6xxx-seriesaluminium alloy has Fe maximum 0.50%, Mn maximum 0.40%, Si maximum0.60%, Mg at least 0.40 to not more than 0.8%, Fe/Mn ratio of <1.75.